Homogeneous ruthenium catalysts useful in the selective reduction of nitroaromatics to amines

ABSTRACT

The invention concerns the use of solubilized ruthenium complexes as homogeneous hydrogenation catalysts for the selective and sequential reduction of dinitroaromatic and mononitroaromatic mixtures to the corresponding amines. A typical embodiment is the reduction of one of the two nitro groups in dinitrobenzene contained in the mixture of dinitrobenzene and nitrobenzene.

Knifton et al.

M. Suggitt, Wappingers Falls, both of N.Y.

Assignee: Texaco Inc., New York, NY.

Filed: Apr. 22, 1974 Appl. No.: 462,912

Related U.S. Application Data Continuation-impart of Ser. Nos. 121,132,March 4, 1971, Pat. No. 3,832,401, and Ser. No. 193,204, Oct. 31, 1971,abandoned.

U.S. Cl 260/580; 252/431 Int. Cl C07c 85/11 Field of Search 260/580 51Sept. 2, 1975 [56] References Cited UNITED STATES PATENTS 3,110,74711/1963 Mullineaux 260/580 X 3,694,509 9/1972 Rylander et al. 260/580 XPrimary Exdmiher-Pau1 F. Shaver Attorney, Agent, or Firm-T. H. Whaley;C. G. Ries; Bernard Marlowe [5 7] ABSTRACT The invention concerns theuse of solubilized ruthenium complexes as homogeneous hydrogenationcatalysts for the selective and sequential reduction of dinitroaromaticand mononitroaromatic mixtures to the corresponding amines. A typicalembodiment is the reduction ofone of the two nitro groups indinitrobenzene contained in the mixture of dinitrobenzene andnitrobenzene.

12 Claims, No Drawings This invention is a continuation-in-part of Ser.No. 121,132, filed Mar. 4, 1971 and now US. Pat. No.

3,832,401 and Ser. No. 193,204, filed Oct. 31, 1971 now abandoned.

BACKGROUND OF THE INVENTION This invention concerns the use ofhomogeneous catalysts to sequentially reduce nitroaromatic substrates totheir corresponding amines. More particularly, this invention concernsthe use of certain solubilized ruthenium complexes as homogeneoushydrogenation catalysts for the sequential reduction of nitroaromatic,polynitroaromatic, nitropolynucleararomatic andpolynitropolynucleararomatic mixtures.

More specifically, this invention concerns the use of solubilizedruthenium complexes as homogeneous hydrogenation catalysts for theselective and sequential reduction of dinitroaromatic, mononitroaromaticmixtures to the corresponding amines.

Many compounds of ruthenium have been described in the literature, someof which have been proposed as catalysts for the homogeneoushydrogenation of organic compounds. Nevertheless, a recent review of homogeneous catalyses for hydrogenation reactions* appears to document thepaucity of reported reductions of nitroaromatics. *Lyons ct a1 Ind. Eng.Chem. Prodv Res. Develop, Vol. 9, p. l Manl. 1970 Recently, in relatedwork (Ser. No. 121,132, filed 3/4/72) it was reported that ahydrogenation process using homogeneous metal complexes, particularlyligand stabilized ruthenium and iron complexes, as catalysts for thehydrogenation of nitroaromatics to aromatic amines. These homogeneouscatalysts were shown to hydrogenate nitroaromatics at room temperaturewith hydrogen pressures below 20 atmospheres, at especially highsubstrate-to-catalyst molar ratios (exceeding 200), and whoseselectivity to amine generally ranges from about 85% to 100%.

It has now been found that certain ruthenium complexes and, inparticular, complexes of ruthenium containing 'rr-Acceptor (1T-Acid)*ligands, exhibit an unexpected selectivity when used as catalysts in thehydrogenation of mixtures of nitroaromatics, nitropolynucleararomatics,polynitroaromatics or polynitropolynucleararomatics. This is especiallytrue in mixtures of mononitroaromatics and dinitroaromatics.

*For a discussion of 1'r-Acccptor (Tr Acid) ligands sec: Advanced lnorganic Chemistry, 2nd Ed. Ch. 27 by F. A. Cotton & G. Wilkinson,Intcrscicnce Publishers 1966.

As far as can be seen from a reviewof the current literature, theinstant invention is believed to represent the first illustration of acatalyst system, heterogeneous or homogeneous, for this type ofsequential hydrogenation. Smith,for example, in a review of thecatalytic hydrogenation of nitro compounds** reports no such selectivitywith Raney nickel and platinum heterogeneous catalysts. Similarly,though both Calderazzo et al*** and S. Murahashi and S. Horie*** reportthe reduction of nitrobenzene to aniline using soluble car bonylcatalysts under stringent reaction conditions of temperature andpressure, neither group of workers has reported the sequentialhydrogenation of nitroaromatic mixtures. **H. A. Smith & W. C. Bedoit..lr., Catalysis" Vol. III, P. 149 1955 ***Calclerazzo et a1 Inorg. Chem.9, 342 (1970) ****Murahashi et a1 Bull. Chem. Soc. Japan, 33, 78 (1960)In view of the aforementioned deficiencies of both heterogeneous andhomogeneous catalysts in the hydrogenation of nitroaromatics, thecatalysts of this invention represent a substantial advance in the art.

According to the invention, a process for the sequen tial homogeneoushydrogenation of a nitroaromatic mixture as hereinafter defined,comprises contacting the substrate mixture with hydrogen in the presenceof a solution containing as catalyst a soluble ruthenium compoundcontaining one or more 'rr-Acceptor (w-Acid) ligand, and arresting thereaction when the substrate mixture has reacted the desired degree ofhydrogenation.

Sequential hydrogenation within the broad context of this inventionmeans the reduction of specific nitro (NO-, groups of nitroaromatic,polynitroaromatic, nitropolynucleararomatic orpolynitropolynucleararomatic substrates to the desired amines with theexclusion of other nitro groups. However, these other nitro groups mayalso be reduced to amine following substantial completion of the initialdesired nitro reduction reaction. For example, the ruthenium complexesdescribed in this invention may be used to reduce one of more nitrogroups to amine in preference to the other or others, provided that thehydrogenation is arrested at a suitable stage. In some instances, between 80 and of one type of nitro group may be hydrogenated before theothers begin to react. It will be appreciated, however, that should thereaction be allowed to proceed unchecked, in most cases all the nitrogroups present would eventually be reduced to amine, and the effect ofthe selectivity of the ruthenium catalysts would then be lost.

Sequential hydrogenation as defined herein, in a much more specific andfavored manner, describes a process for the reduction of dinitroaromaticsubstrates contained in mixtures of the dinitroaromatics withmononitroaromatics. Thus the initial reaction which takes place isselective reduction (or hydrogenation) of one nitro group of saiddinitroaromatic to a product containing one nitro group and one aminogroup. As can be appreciated by this discourse this sequential processdiffers from the conventional hydrogenation broadly defined above, inthat it requires:

a. mixtures of dinitroaromatics and monoaromatics,

b. empirically determined parameters which may well differ from thoseemployed in conventional hydrogenation using the same catalysts, and

c. a more selective or restrictive group of ruthenium catalysts whichare capable of hydrogenating between about 80 to about 95% of one nitrogroup of the two available nitro groups in thedinitroaromaticmononitroaromatic substrate mixture without signifcantlyhydrogenating (less than 10%) either the second nitro group of thedinitroaromatic component and/or the sole nitro group of themononitroaromatic compo nent of the mixture.

Here the invention is illustrated, but not limited, by equations 1 and2. Starting with a mixture of A and B the initial reaction l isselective reduction of A to the mononuclear aromatic product containingone amino group and one nitro group. B remains unreduced until reaction1 is substantially complete. In this instance it is only when about 80to 95% of A has been selectively reduced that hydrogenation of themononitroaromatic starts to take place.

Equation It is an object of this invention to provide recent but knownhomogeneous transition metal complexes, espe cially complexes ofruthenium and mixtures thereof, which will sequentially hydrogenate di,nitroaromatic, polynitroaromatic, nitropolynucleararomatic andpolynitropolynucleararomatic mixtures in mixtures of dinitroaromaticswith the aforementioned components. The sequential hydrogenation of thisprocess falls within certain general classes which include:

a. The selective hydrogenation of polynitroaromatics in preference tonitroaromatics or intermediate nitroaromatic amines, for example, theselective hydrogenation of p-nitrobenzene to p-nitroaniline in thepresence of nitrobenzene and the p-nitroaniline as shown above.

b. The selective hydrogenation of nitropolynucleararomatics inpreference to nitroaromatics, e.g. the reduction of l-nitronaphthaleneto a-naphthylamine in the presence of nitrobenzene or:

c. The selective hydrogenation of polynitropolynucleararomatics in thepresence of nitropolyaromatics in the intermediatenitropolynucleararomatic amines, e.g. the reduction of1,4-dinitronaphthalene to 4-nitro-1- naphthylamine in the presence ofl-nitronaphthalene.

f. The selective hydrogenation of 2,6-dinitrotoluene in the presence ofp-nitrotoluene.

g. The selective hydrogenation of small concentrations ofm-dinitrobenzene present in crude nitrobenzene produced by benzenenitration.

Further illustrative embodiments of this invention may be found in theaccompanying examples. Other objects will become apparent to thoseskilled in the art after a perusal of this application.

In practice, the above objects, among others, will be achieved by thefollowing procedure or minor modifications thereof:

In the broadest contemplated practice,

a. at least a molar excess of a nitroaromatic, polynitroaromatic,nitropolynuclear, polynitropolynucleararomatic or dinitroaromaticmixture of substrates to be reduced is admixed in the absence ofoxidizing conditions with a catalytic amount of a ruthenium complex in asubstantially non-aqueous, inert solvent media, sufficient to at leastpartially solubilize said substrate and catalyst to form a reactionmedia,

b. then said reaction media is heated from at least about 20C andupwards under superatmospheric pres- H O N 6? N0 0 N 0 NH Q 110 L;substantially unchanged sures in the presence of at least astoichiometric quantity of hydrogen (with respect of nitroaromatic sub-.

strate) until substantial reduction of at least one of the nitroaromaticsubstrates to the corresponding amine or nitroamine takes place, and

c. the amine contained therein is separated.

In the favored practice a substantially anhydrous, deoxygenated,substantially non-aqueous reaction mixture comprising the nitroaromaticsubstrates is formed by:

a. admixing at least a 5 molar portion* of a nitroarosubstantiallyunchanged matic, nitropolynucleararomatic, polynitroaromatic orpolynitropolynucleararomatic mixture with one molar portion of at leastone ruthenium catalyst complex, in the presence of sufficient inertsolvent media to at least partially solubilize said substrate andcatalyst, said solvent media being selected from the group consisting ofessentially neutral media, alkaline and acidic media, said reactionmixture being substantially free of oxidizing agents,

*These 5 molar figures represent proportions or ratios of the substrateto the catalyst rather than absolute numbers b. heating said reactionmixture while free from oxidizing agents between about 20 and 160C underinitial superatmospheric pressures ranging from about 100 psig andupwards, said pressure being supplied by at least a stoichiometricexcess of gaseous hydrogen (with respect to nitroaromatic substrate inthe mixture), said heating taking place in a substantially anhydrousenvironment, for at least a time sufficient to substantially reduce atleast one of the said nitroaromatic substrates to its correspondingamine or nitroamine and c. isolating said amine or nitroamine containedtherein.

In the preferred practice, at least one nitro group of dinitroaromaticsubstrate present in a non-aqueous so]- I vent media containing amixture of dinitroaromatic and mononitroaromatic substrates, is reducedto the corresponding amine by the process consisting essentially of:

a. admixing a dinitroaromatic substrate selected from the groupconsisting of p-dinitrobenzene, m dinitrobenzene, l,4-dinitronaphthalene, l ,3- dinitronaphthalene, dinitrodurene,2,6-dinitrotoluene, 3,4-dinitrotoluene and 3,5-dinitro--xylene,

b. with a mononitroaromatic substrate selected from the group consistingof nitrobenzene, p-nitrotoluene, -nitro-0xylene, 3-nitro-O-xylene,2-nitromesitylene,

l-nitronaphthalene, 9-nitronaphthalene, l-nitro-4- cyclohexylbenzene,2-nitrobiphenyl and 4- nitrobiphenyl,

c. and at least a catalytic amount of homogeneous soluble rutheniumcatalyst selected from the group consisting of RuCl (P(C H (Ru(CO) Cl-2( )2( s s)a)2, 2( 6 s)3)3, RuCl (P(C H and RuCl (CH )(C l-l PBr,

d. in non-aqueous, non-oxidizing solvent media, in a pressurizedatmosphere with hydrogen gas sufficient to hydrogenate said nitro groupof the dinitroaromatic substrate to the corresponding amine, to form areaction mixture,

e. and heating said pressurized reaction mixture at superatmosphericpressures ranging from about 100 psig to about 2,000 psig, attemperatures ranging from about 50C to about 135C until about 80-95% ofsaid nitro group of the dinitroaromatic substrate is reduced to thecorresponding amine.

The stage of the hydrogenation at which the process should be arrestedmay be readily determined by experiment. For example, a mixed substratemay be hydrogenated under carefully controlled conditions using theprocess of this invention, and the product analyzed at regularintervals. The results of these analyses may then be plotted on a graphfrom which it may be readily deduced at what stage the maximumconcentration of the required product will be present in the mixture.The product mixture may be analyzed by any convenient technique, butgas/liquid chromatography methods are preferred.

Once the pattern of the sequential hydrogenation of a particular mixedsubstrate with a particular ruthenium catalyst has been established,hydrogenation may be arrested at the appropriate time by rapiid coolingof the reaction mix and by removal of the remaining hydrogen gas.

In order to aid in the full understanding of the inventive concept, thefollowing additional disclosur is submitted:

A. NITROAROMATIC SUBSTRATES Any aromatic substrate containing from 6 to30 carbon atoms, or more, and containing at least one nitro (N0 groupper molecule may be employed. These include the mononuclearmononitroaromatics such as nitrobenzene, nitrotoluenes, nitroxylenes aswell as the dinuclear, trinuclear and higher (polynuclear) mononitroaromatics such as l-nitronaphthalene and 5- nitroanthracene. Thediand trinitro aromatics, that is di-, trinitrom ononuclear compoundssuch as mdinitrobenzene and its congeners may also be substrates, inaddition to di-, tri tri and polynitropolynuclear aromatics such as l,9- dinitronaphthalene and its homologues and, where they are available,nitro steroids. The nitro group need not be directly bonded to thearomatic ring but can include derivatives such as nitro-benzyl, whereinthe nitro group is attached to an alkylene group and separated from anaromatic nucleus by groups containing 1 to 3 carbon atoms. Inasmuch asthe starting materials are more readily available at lower costs, thefavored nitroaromatic substrates are those wherein from 1 to 3 nitrogroups are bonded to mono, dior trinuclear (benzene) ring systemscontaining from 0 to 3, particularly 0 to 4, alkyl groups per ring. Thenitrated aromatics can be derived from any number of different nitrationprocedures, such as vapor-liquid phase nitration, liquidliquidprocedures, etc. The substrate can be in the form of nitrated aromaticscontaining substantial quantities of non-nitrated aromatics or theirmixtures, neat or containing other inert solvents or diluents, such asparaffins, ethers, and the like.

The preferred nitroaromatic substrates of this inven tion are thenitroaromatic substrates which may contain from 6 to 30 carbon atoms, ormore, and at least one nitro (N0 group per molecule. The dinitroaromaticsubstrates may contain the two nitro groups bonded to carbon atoms atthe ortho, meta, or para ring positions, may contain additional alkyl oraryl substituents, and be part of a polynuclear aromatic ring system.Examples include p-dinitrobenzene, mdinitrobenzene, l,4-dinitronaphthalene, 1,3- dinitronaphthalene, dinitrodurene,2,6-dinitrotoluene, 3,4-dinitrotoluene and 3,5-dinitro-o-xylene.

The mononitroaromatic substrate may also contain additional alkyl oraryl groupings and be mononuclear or polynuclear aromatics. Examplesinclude nitrobenzene, p-nitrotoluene, S-nitro-m-xylene, 3-nitro-oxylene,2-nitromesitylene, l-nitronaphthalene, 9- nitroanthroacene,l-nitrobiphenyl and 4-nitrobiphenyl.

B. CATALYSTS SYSTEM The homogeneous catalysts of this invention areselected from complexes of ruthenium, containing ruthenium in varyingoxidation states, usually between zero and +4, and prepared by the welldocumented references in the technical literature. The ruthenium complexmust contain one or more 1r-Acceptor ('IT-ACld) ligands. Particularlyfavored are ligands containing a donor atom of Group IVB, Group VB orGroup VIB. Examples include the organic substituted phosphine or stibeneligands such as PR; or SbR where R represents hydrocarbyl radicals whichmay be the same or different, e.g. alkyl, aryl, alkanyl, aralkyl orcycloalkyl and those derived from the quaternary phosphonium ion such as[PR4l+- Alternatively, the ruthenium complex may contain one or moreother 'rr-Acceptor ligands such as carbonyl (CO), substituted carbonylor nitrosyl, either alone, or in addition to the ligand or ligandscontaining a donor atom of Groups IVB, VB or VIB. Suitable anionicligands include Cl, Br, CN, NCO, and CH COO. Halogens are the preferredanionic ligands.

Illustrative ruthenium complexes which function effectively as selectivereducing agents in this process include RuCl (P(C ,-l-l RuCl(P(C I-I 2(6 5)3)3 3( )3)2,

*Et is used as a symbol for the CH;,CH -radical In contrast to Ser. No.121,132 filed March 4, 1971, now US. Pat. No. 3,832,401, iron complexeswhich contain 1r-Acceptor ligands, such as Fe(- CO);,(P(C I-I do notfunction as selective hydrogenation catalysts for mixed nitroaromaticsubstrates, and so are not suitable as catalysts in this process.Ruthenium complexes which do not contain 1rAcceptor (Tr-Acid) ligands,such as ruthenium acetylacetonate and ruthenium naphthenate, are alsonon-selective and therefore unsuitable catalysts for this process.

Preferably, but not necessarily, the ruthenium catalyst is one whichcontains displaceable ligands. However, in some instances it isdesirable to use a solvating agent to convert the ruthenium compound toa more soluble form. The solvating agent usually comprises a polarsolvent having an active hydrogen atom preferably contained in ahydroxyl group. Suitable solvating agents include the lower alkanolssuch as ethanol and propanol, cycloaliphatic or aromatic alcohols andphenols, as well as the mixtures of these alkanols and aromatics eitherin the neutral or alkaline state.

It is thought, without limiting the invention thereby, that thesolvating agent functions by promoting conver sion of the rutheniumcompound catalyst to a hydrido species, which is soluble in the liquidmedium used.

It is not essential that all of the ruthenium compound shall be insolution at the beginning of the reduction provided that at least acatalytic amount is present. A catalytic amount as defined herein refersto an amount sufficient under the appropriate combination of temperatureand pressure parameters to initiate the desired reduction. In theinstance of ruthenium, if at least 0.0001 moles, preferably at least0.001, of ruthenium per mole of nitroaromatic are present, catalysiswill take place. Higher ratios of catalyst to substrate give more rapidconversions although ratios of 0.1 or more are disadvantageous in thatthey are costly and entrap or entrain product, unnecessarilycomplicating isolation and purification. 7

The mole ratio of nitroaromatic substrates to homogeneous rutheniumcatalyst should not exceed about 1000: l especially to achieve optimumyields, within a reasonable period of time without having reproducibiLity problems. As previously disclosed ratios of the individualnitroaromatic substrate to catalyst lower than about 10:1 are to beavoided if the aromatic amine product is: to be isolated. For the bestbalance of yield to reactit -n time, ratios varying from about 10:] to:1 o each nitroaromatic substrate to catalyst, should be employed. I

C. INERT DILUENT AND SOLVENTS The novel reduction process can be runmost readily in the presence of sufficient inert diluent to form ahomogeneous single-phase reaction mixture. Since a homogeneous, oruniform, reaction mixture offers the most convenient vehicle in which torapidly and selectively reduce the nitroaromatics to amines in goodyield, the use of inert solvent is employed. Generally speaking, anyorganic liquid in which the nitroaromatic substrate and catalyst aresoluble and which is inert to reduction under the conditions of theinventive process, can be used as a diluent. These include the alkylesters, such as diethyl ether, the C to C alkanols, the hydroxylatedethers, chlorinated hydrocarbons such as methylene chloride, aromaticssuch as benzene, toluene and xylene, as well as their mixtures with orwithout alkaline or acid agents. The choice of whether to use an acidic,alkaline or neutral polar solvent system depends primarily upon thenitroaromatic to be reduced.

D. REDUCING ATMOSPHERE Insofar as can be determined, the homogeneouscatalyst, possibly in some intermediate, more active form, abstractshydrogen from the environmental, hydrogen atmosphere. While nitrogen,methane, ethane, or inert gases such as helium, argon or neon may bepresent in small proportions, (less than 30% by volume) withoutadversely effecting conversions or yields, their presence appears tooffer no concurrent advantages and, therefore, is to be avoided.

Ordinarily, a reaction vessel capable of being pressurized, agitated,heated and cooled is charged with all of the components of the reactionmixture i.e. the nitroaromatic mixture, catalyst system, solvents, etc.These components either individually or collectively are flushed withinert gas such as argon or nitrogen because of their known sensitivityto oxidizing agents such as air. The residual flushing or purging ofinert gaseous environment is conveniently accomplished with hydrogen ornitrogen andthe reaction mixture is pressurized initially to the desiredextent and heated in a substantially hydrogen atmosphere until thedesired reduction to aromatic amine takes place.

E. REDUCTION TEMPERATURE The reaction temperature for reduction is inmany ways quite flexible. At temperatures below about 20C, however, therate of reduction of substrate to the amine is quite slow, while attemperatures much above 160C yields fall off sharply, probably due tocatalyst decomposition, and for this reason these temperatures in excessof 160C are to be avoided. Since good results have been obtained between35C and 160C these are favored. Inasmuch as the best yields of aminehave been obtained at reduction temperatures between about 50C and C atsuperatmospheric pressures, when the preferred homogeneous rutheniumcomplexes are used as catalyst, these temperatures represent thepreferred temperature range. I

F. REDUCTION PRESSURES Pressures of hydrogen greater than atmospheric (0psig) are required to obtain reasonable rates of reduction at reactiontemperatures above 35C. Superatmospheric hydrogen pressures ranging fromabout 100 psig to about 2000 psig, coupled with temperatures of about35C to l35C consistently give the best yields within reasonable reactiontimes and for this reason are preferred.

G. REACTION TIMES FOR SUBSTANTIAL RE- DUCTION The time required forsubstantial reduction of the nitroaromatics to the corresponding aminesis a variable, dependent primary upon the temperature and pressureemployed, the choice of catalyst and nitroaromatic substrate mixture tobe reduced, and the ratio of substrate to catalyst system employed,among other factors. Ordinarily the reaction times will vary betweenabout 10 minutes to 24 hours, according to whether all the nitro (NOgroups present are to be hydrogenated to amine, or whether someintermediate species are to be isolated. In the latter instancesreaction times range between about 20-360 minutes.

H. EXPERIMENTAL PROCEDURE The reductive process is ordinarily performedas follows:

A conveniently sized reactor fitted with gas inlet, condenser, stirring,heating and pressurizing means, is charged with catalyst solution,preferably deoxygenated during charging, and containing thenitroaromatic substrate mixture and inert solvent. Deoxygenation can beaccomplished by a hydrogen or nitrogen flush of the reaction mixture.The agitated reaction mixture is sealed and heated to above 20C undersuperatmospheric pressure provided by hydrogen under pressure.

The rate of hydrogenation may be monitored by gas chromatographyanalysis, and reduction arrested at the appropriate point by rapidlycooling the reaction mixture, and bleeding off the remaining hydrogengas.

Work-up of the product mixture is as follows:

The mixture of amine product, unreacted nitroaromatics, rutheniumcomplex catalyst and light solvent is stripped under reduced pressure toremove the volatiles, and the spent ruthenium catalyst is filtered or removed by centrifugation. The aromatic amine product contained in thefiltrate is then recovered by one or more of the methods used toseparate amines from contaminants. For example, the amine can be steamdistilled or extracted with mineral acid. In the latter case, the aminesalt is converted (sprung) to the free amine by neutralization with abasic material.

In any event, the amine product can be further purified or used asobtained, dependent upon product application. In general, the amines areidentified by gas chromatography (ge), infrared spectra (ir) and/ornuclear magnetic resonance (nmr) spectra.

Having described the inventive process in general terms, the followingexamples are submitted to supply specific illustrative embodiments.Unless otherwise specified, all temperatures are in centigrade and allparts are by weight rather than by volume.

EXAMPLE 1 THE SEQUENTIAL HYDROGENATION OF NITROBENZENE-p-DINITROBENZENEMIXTURE USING RuCl [P(C.;H,-,) AS CATALYST To a suitable autoclave-typereactor provided with pressurizing, heating, cooling, agitating anddistillation means is charged 100 ml of a deoxygenated l:l equivolumesolvent mixture of benzene and ethanol containing the tris(triphenylphosphine) ruthenium (II) chloride catalyst (0.38 g, 0.4mmoles), and equimolar quantities of nitrobenzene (1.02 ml, l mmoles)and p-dinitrobenzene (1.68 g, mmoles). After sealing the solutionmixture under an initial nitrogen pressure of 100 psig, and heating to120C, hydrogen gas is introduced into the reactor to a partial pressureof 1,200 psig, and the reduction of the nitroaromatics followed by gcanalyses of samples withdrawn at regular time intervals. The progress ofthe hydrogenation may be seen from the results in Table I'below:

TABLE I THE SEQUENTIAL HYDROGENATION OF A NITROBENZENE- p-DINITROBENZENEMIXTURE CATALYZED BY 2( u r ):i):i

CONVERSION OF:

It will be seen that:

1. At least of the p-dinitrobenzene is hydrogenated to p-nitroanilinebefore a measurable amount of nitrobenzene has been converted toaniline.

2. About 30% of the nitrobenzene is hydrogenated to aniline before asignificant amount of pnitroaniline intermediate has been converted topphenylenediamine.

Should it be desired to isolate the intermediate reduction products,hydrogenation may be arrested at the appropriate time by cooling andbleeding off the excess hydrogen gas. The recovered product solution isthen concentrated by removing the light solvents, and the precipitatedruthenium catalyst. The latter is filtered off and recovered as a brownsolid, which is washed with a fraction of petroleum ether and air dried.The nitroamine or diamine products may be isolated either bydistillation or acid extraction.

EXAMPLE 2 THE SEQUENTIAL HYDROGENATION OF NITROBENZENE-m-DINITROBENZENEMIXTURE USING RuCl [P(C -I'I The procedure of Example I is followedusing an equimolar substrate mixture of nitrobenzene (1.02 ml, 10mmoles) and m-dinitrobenzene (1.68 g, 10 mmoles) in a 1:1ethanol/benzene solution.

The results of the hydrogenation are given in Table II.

It will be seen that some 95% of the mdinitrobenzene is hydrogenated tom-nitroaniline be fore the m-nitroaniline so produced or thenitrobenzene already present have begun to react.

This result, and that of Example I, confirms that the RuCl (P(C,,Hhomogeneous catalyst will selectively hydrogenate polynitroaromaticssuch as dinitroaromatics in preference to nitroaromatics such asmononitrobenzene and the intermediate nitroaromatic amines.

TABLE II TABLE IV SEQUENTIAL HYDROGENATION OF A NITROBENZENE-m-DINITROBENZENE MIXTURE CATALYZED BY SEQUENTIAL HYDROGENATION OF ANITROBENZENE- pDINITROBENZENE MIXTURE CATALYZED BY RUC]2( P(C11H5):1):15 RUCIJCO P( CGHS CONVERSION OF: CONVERSION OF: Time fromm-Dinitrobenzene Nitrobenzene m-Dinitro- Time from p-Dinitrobenzenep-Nitroaniline Nitro- Start to m-Nitroto Aniline benzene to Start top-Nitroto p-Phenybenzene (Min.) anilines (VI) (71) m-Phenylene- (Min.)aniline (7r) lenediamine (7r) to Aniline diamine (71) (71) 20 54 1 1 1013 1 1 40 69 1 1 20 24 1 1 60 79 1 1 40 51 1 1 90 88 1 1 80 61 1 1 12095 2 1 120 711 1 1 150 99 4 1 I60 92 1 1 I80 9 1 200 99 1 4 240 33 16240 99 1 13 280 99 1 22 320 99 2 31 360 99 3 40 EXAMPLES 3 TO 8 THESEQUENTIAL HYDROGENATION OF NITROBENZENE-p-DINITROBENZENE TABLE vMIXTURES USING CERTAIN OTHER RUTI-IENIUM CATALYSTS SEQUENTIALHYDROGENATION OF A NITROBENZENE- Ut1l1z1ng the apparatus, reductlonprocedure and p-DINITROBENZENE MIXTURE CATALYZED BY equimolarnitrobenzene, p-dinitrobenzene substrate RUCMSMCIHW) mixture of Example1, various ruthenium complexes CONVERSION OF; were employed asSequential hydrogenation catalysts in Time from p-Dinitrobenzenep-Nitrouniline Nitrobenzene th bj t li i Start to .1-Nit? top-Phenyleneto Aniline M '1' d" v 7 As can be seen from the data 1nTables III to VI, the m Am me mine U I) p-dinitrobenzene fraction ispreferentially hydroge- 20 23 1 1 nated to p-nitroaniline to thesubstantial exclusion both 40' 48 60 1 76 1 1 of the mtrobenzene and thep-n1troan1l1ne Intermed1ate 70 83 1 2 with the following types ofcatalyst. 1:8 1 6 4 a. The ruthenium (II) tncarbonyl dimer [Ru(- 150 99l 59 CO):ICI2]2 180 99 6 79 b. The triphenylphosphine ruthenium (II)carbonyl 99 69 96 300 99 88 99 2( )2[ s .=-)3]2 c. The triphenylstibeneruthenium (II) complex 2( 1; s):I):Il 40 d. The ruthenium (Ill)triphenylphosphine complex TABLE VI RUC]:I( P(C11H5)3)2 No such selectity as fo th: SEQUENTIAL HYDROGENATION OF A NITROBENZENE- Rutheniumacetylacetonate p-DINITROBENZENE MIXTURE CATALYZED BY R I -H b.Ruthenium naphthenate UCMHC" 1 With these two latter complexes thenitrobenzene CONVERSION OF: and p-dinitrobenzene fractions were reducedconcur- Tins: from p-Dinitrclllbenzene p-Nilg'loanilline b Nitrotart topitroto peny eneenzene to rently, with some dIfference In rate. (Min.)aniline (,7?) diamine (7C) Aniline (70) The result confirms that onlycertain ruthemum complexes containing one or more 1r-Acceptor (1r-Acid)f :8 ligands will sequentially hydrogenate mixtures of 20 98 l 2polynitroaromatics and nitroaromatics. 40 99 1 6 80 99 1 16 TABLE III120 99 1 26 1110 99 1 43 SEQUENTIAL HYDROGENATION OF A NITROBENZENE-p-DINITROBENZENE MIXTURE CATALYZED BY l ):1 2l2 CONVERSION OF: EXAMPLES9 1 1 Time from p-Dinitrobcnzene p-Nitroaniline Nitrobenzene THE NONSELECT[VE HYDROGENATION O]:

Stt t N't 1 -Ph 1 t A '1 i, ,,1 ;j, 1,, ,{f,f, 623NITROBENZENE-p-DINITROBENZENE MIXTURE USING IRON CATALYSTS 2o 6 1 1 4014 1 1 The procedure of Example I was repeated using the g8 sameequimolar nitrobenzene, p-dinitrobenzene sub- 100 111 1 1 strate mixtureand bis(triphenylphosphine) iron tricar- 120 99 1 5 '50 99 1 14 bonyl In1.1 benzene, ethanol as the homogeneous cat- I 99 1 23 alyst. 240 41 Theresults of the h dr ena 300 99 5 59 y og on are gIven In Table VII.

It can be seen that the p-dinitrobenzene and nitrobenzene fractions arereduced concurrently, the latter at a somewhat slower rate. However, itshould be noted that the p-nitroaniline intermediate is not furtherreduced until essentially all the p-dinitrobenzene has been partiallyhydrogenated.

A similar result was found with:

1. iron naphthenate;

2. iron acetylacetonate.

TABLE VII HYDROGENATION OF A NITROBENZENE- p-DINITROBENZENE MIXTURECATALYZED BY l:i( n r,)a 2

CONVERSION OF:

Time from p-Dinitrobenzcne Nitrobenzene p-Nitroaniline Start to p-Nitroto Aniline to p-Pheny- (Min.) aniline ("/z) ("/r.) lenediamine IO 34 4 120 56 8 1 40 80 I6 1 60 93 24 l 80 99 32 3 I20 99 47 I6 I60 99 63 28 20099 78 47 240 99 92 69 Iron complexes and salts are therefore notsequential hydrogenation catalysts for the reduction of nitroaromatic,polynitroaromatic mixtures to amine.

EXAMPLE l2 THE SEQUENTIAL HYDROGENATION OF NITROBENZENE- l-NITRONAPHTHALENE MIXTURE USING RuCl [P(C H,-,)

The procedure of Example 1 was followed using the same catalyst but asubstrate comprising an equimolar mixture of nitrobenzene (1.02 ml, 10mmole) and nitronaphthalene 1.73 g. 10 mmole) in equivolume benzene,ethanol solution.

The results of the hydrogenation are summarized in Table VIII. Here itcan be seen that l-nitronaphthalene is selectively reduced toa-naphthylamine, at least up to 40% conversion of the nitronaphthalene.Beyond the 40% conversion point, however, reduction of bothnitrocompounds takes place concurrently.

TABLE VIII SEQUENTIAL HYDROGENATION OF A NITROBENZENE-I-NITRONAPHTI'IALENE MIXTURE CATALYZED BY 2( |z :,):u).1

CONVERSION OF:

Time from l-Nitronaphthalenc Nitrohcnzcne to Start (Min.) toa-Naphthylaminc Aniline (7r) IO 16 1 20 28 1 30 38 2 4o 46 3 50 52 6 6O58 IO EXAMPLE I3 THE SEQUENTIAL HYDROGENATION OF Z-NITROMESITYLENE- l-NITRONAPHTHALENE MIXTURE USING RuCl (P(C H,-,) AS CATALYST Theprocedure of Example 1 was followed using a 10 mmoles each of a.nitroaromatic mixture of 2- nitropolynucleararomatic mixtures.

TABLE IX l-nitronaphthalene SEQUENTIAL HYDROGENATION OF AZ-NITROMESITYLENE- I-NITRONAPI'ITHALENE MIXTURE CATALYZED BY 2( issl:i):i

CONVERSION OF:

Time from l-Nitronaphthalene to 2Nitromesitylene Start (Min.)aNaphthylamine (71) to Mesidine (71) 2O 47 1 40 l 6O 77 I 80 87 l I00 2I20 99 6 180 23 270 55 EXAMPLE 14 THE SEQUENTIAL HYDROGENATION OFZ-NITROMESITYLENE l-NITRONAPHTHALENE MIXTURE USING RuCI (CO)- (P(C H,-,)AS CATALYST In this example, the apparatus and reduction procedure ofExample I were used with 0.4 mmole (0.29 g) of the ruthenium complexRuCl (CO) P(C ,H dissolved in 100 ml of equivolume benzene ethanolcontaining 10 mmole each of 2-nitromesitylene and lnitronaphthalene, asthe charge solution. The progress of the hydrogenations, which were runat C, is shown in Table X.

It is apparent that at least 96% of the lnitronaphthalene fraction maybe reduced to oz-naphthylamine with this catalyst prior to any noticablereduction of the 2-nitromesitylene.

TABLE X SEQUENTIAL HYDROGENATION OF A NITROMESITYLENE- NITRONAPHTHALENEMIXTURE CATALYZED BY fl lgl n a):x)2

CONVERSION OF:

Time from l-Nitronaphthalene to Z-Nitromesitylene Start (Min.)aNuphthylamine ((4) to Mesidine (71) 30 o l 60 l I 1 90 I8 1 I20 25 lI80 39 l 240 57 1 300 76 1 360 96 l EXAMPLE THE NON-SELECTIVEHYDROGENATION, 0

2-NlTRO-MESITYLENE-1-NITRONAPHTHALENE MIXTURE USING RUTHENIUMAcETYLAcEToNATE As CATALYST TABLE XI HYDROGENATION OF A NITROMESITYLENBNITRONAPHTHALENE MIXTURE CATALYZED BY RU(CH;,COCHCOCH,,);,

CONVERSION OF:

Time from I-Nitronaphthalenc 2 Nitromesitylcne Start (Min.) to 2Naphthylaminc to Mcsidine ("/1) EXAMPLE 16 THE NON-SELECTIVEHYDROGENATION OF Z-NITROMESITYLENE-l-NITRONAPHTHALENE MIXTURE USINGFe(CO);;(P(C I-I,.-,) AS CATALYST Here the hydrogenation procedure ofExample I. and the charge stocks of Examples l3l5 were used. butsubstituting Fe(CO) P(C H as catalyst. The hydrogenation data aresummarized in Table XII.

It can be readily seen that Fe(CO) (P(C l-I is nonselective for thehydrogenation of nitroaromatic, nitropolynucleararomatic mixturesalthough the two fractions may be reduced to amine at somewhat differentrates.

TABLE XII HYDROGENATION OF A NITROMESITYLENE NITRONAPHTHALENE MIXTURECATALYZED BY FC(CO);;( u s):;):

CONVERSION OF:

Time from l-Nitronaphthalcnc Z-Nitromcsitylcnc Start (Min.) tol-Naphthylaminc to Mcsidinc (71) EXAMPLE 17 I THE SEQUENTIALHYDROGENATION OF I -NITRONAPHTI- IALENE-P-DINITROBENZENE MIXTURE USINGRuCl P(C l-I AS CATALYST The procedure of Example I was repeated usingthe same catalyst composition but 10 mmole each of lnitronaphthalene andp-dinitrobenzene. The progress of the hydrogenations is shown in TableXIII. it can be seen from the data in Table XHI that at least of thepolynitroaromatic component (p-dinitrobenzene) is hydrogenated to amineprior to any significant reduction of the second, nitropolyaromatic,substrate taking place with this catalyst.

EXAMPLE 18 THE SEQUENTlAL HYDROGENATION OF l-NITRONAPHTHALENE- I ,4-DINITRONAPHTI-IALENE MIXTURE USING RuCl (P(C H AS CATALYST The procedureof Example I was repeated using the same catalyst composition but 10mmole each of lnitronaphthalene and 1,4-dinitronaphthalene. l,4-dinitronaphthalene is selectively hydrogenated toI-amine-4-nitronaphthalene without substantial conversion of thel-nitronaphthalene.

TABLE Xlil SEQUENTIAL HYDROGENATION OF AlNITRONAPHTHALENEp-DINITROBENZENE MIXTURE CATALYZED BY RuCI(P(C,;H,-,);,)

CONVERSION OF1 SEQUENTIAL HYDROGENATION OF NITROBENZENE-p-DINITROBENZENEMTXTURE CATALYZED BY RUTHENIUM CHLOREDE EN COMBINATION WITH A.QUATERNARY PHOSPHONIUM ION The compound, believed to be Rul (CH )(C HPBr] catalyst was prepared by refluxing ruthenium tri chloride (0.4mmole) with the quaternary phosphonium salt. methyltriphenylphosphoniurn bromide (1.2 mmole) in benzene-ethanol. The resulting greencat lyst solution so prepared was used in the hydrogenation of anequimolar nitrobenzene, p-dinitrobenzene mixture (IO mmole each). Theresults are summarized in Table XIV.

It is apparent that with this catalyst solution, pdinitrobenzene isselectively hydrogenated to pnitroaniline, and only after some 80% ofthe dinitrobenzene charged has been reduced to amine is there anysubsequent reduction of the nitrobenzene component. A solution ofruthenium trichloride alone is nonselective in this application TABLEXIV SEQUENTIAL HYDROGENATION OF A NITROBENZENE- p-DINITROBENZENE MIXTURECATALYZED BY EXAMPLES 20 TO 24 Utilizing the apparatus, reductionprocedure and RuCl [P(C H catalyst of Example 1, the following pairs ofnitroaromatic and dinitroaromatic substrates were hydrogenated to thecorresponding amines according to the subject application:

MONONl- TROAROMATIC COMPONENT EXAMPLE DINITROAROMATIC COMPONENT2,6-Dinitrotoluene O-Nitrotoluene l6 3 ,S-DinitrtrO-xylene2-Nitro-m-xylene l7 Dinitrodurene 2Nitromesitylcne 18 l,3-Dinitronaphthalenc 9-Nitrounthracenc l9 p-Dinitrobe nzene2-Nitrobiphenyl Here, sequential hydrogenation is exemplified formixtures of mononitroaromatic and dinitroaromatic substrates containingboth alkyl and aryl substituents, and having both mononuclear andpolynuclear aromatic ring systems.

As can be seen from the numerous examples and compiled data presented inthe application, various changes, modifications and substitutions can bemade in the claimed process without departing from the inventiveconcept. The metes and bounds of the invention can best be seen by anexamination of the claims which follow, read in conjunction with thepreceding disclosure of this application.

What is claimed is:

l. A process for selectively and sequentially hydrogenating one of twonitro groups of dinitroaromatic substrates contained in a mixture ofnitroaromatic substrates, said process consisting essentially of:

l. admixing one dinitroaromatic substrate selected from the groupconsisting of p-dinitrobenzene, mdinitrobenzene, 1,4-dinitronaphthalene, l ,3- dinitronaphthalene, dinitrodurene, 2,6-

dinitrotoluene, 3,4-dinitrotoluene and 3,5-dinitroo-xylene with onemononitroaromatic substrate selected from the group consisting ofnitrobenzene, p-nitrotoluene, 5-nitro-o-xylene, 3-nitro-o-xylene,2-nitromesitylene, l-nitronaphthalene, 9- nitronaphthalene,1-nitro-4-cyclohexylbenzene, Z-nitrobiphenyl and 4-nitrobiphenyl, in anonaqueous, non-oxidizing solvent media to form a reaction mixture,

2. heating said reaction mixture to be hydrogenated between about 50C toabout 135C, with at least enough hydrogen gas to hydrogenate one nitrogroup of the dinitroaromatic substrate to the corresponding amine, atsuperatmospheric pressures of hydrogen gas ranging from about 100 psigto about 2,000 psig and in the presence of at least a catalytic quantityof a homogeneous, solubilized ruthenium catalyst selected from the groupconsisting of until about to about of said one nitro group ofdinitroaromatic substrate is hydrogenated to the corresponding amine. 2.The process of claim 1 wherein the mixture of nitroaromatics consists ofP-dinitrobenzene and nitrobenzene.

3. The process of claim 1 wherein the mixture of nitroaromatics consistsof m-dinitrobenzene and nitrobenzene.

4. The process of claim 1 wherein the mixture of nitroaromatics consistsof 1,4-dinitronaphthalene and lnitronaphthalene.

5. The process of claim 1 wherein the mixture of nitroaromatics consistsof 2,6-dinitrotoluene and onitrotoluene.

6. The process of claim 1 wherein the mixture of nitroaromatics consistsof pdinitrobenzene and nitronaphthalene.

7. The process of claim 1 in which said solvent media is selected fromthe group consisting of aromatics, alkyl ethers and chlorinatedaliphatic hydrocarbons.

8. The process of claim 1 wherein the non-aqueous solvent media containsa solvent which is a C to C alkanol.

9. The process of claim 1 wherein the ruthenium catalyst is RuCl [P(Cl-l 10. The process of claim 1 wherein the ruthenium catalyst is RuCl(CO) [P(C l-i 11. The process of claim 1 wherein the ruthenium catalystis RuCl [Sb(C l-l 12. The process of claim 1 wherein the ruthenium

1. A PROCESS FOR SELECTIVELY AND SEQUENTIALLY HYDROGENATING ONE OF TWONITRO GROUPS OF DINITROAROMETIC SUBSTRATES CONTAINED IN A MIXTURE OFNITROAROMATIC SUBSTRATES, SAID PROCESS CONSISTING ESSENTIALLY OF: 1.ADMIXING ONE DINITROAROMATIC SELECTED FROM THE GROUP CONSISTING OFP-DINITROBENZENE, M-DINITROBENZENE, 1,4-DINITRONAPHTHALENE,1,3-DINITRONAPHTHALENE, DINITRODURENE, 2,6-DINITROTOLUENE,3,4-DINITROTOLUENE AND 3,5-DINITRO-O-XYLENE WITH ONE MONOITROAROMATICSUBSTRATE SELECTED FROM THE GROUP CONSISTING OF NITROBENZENE,P-NITROTOLUENE, 5-NITRO-O-XYLENE, 3-NITRO-O-XYLENE, 2NITROMESITYLENE,1-NITRONAPHTHALENE, 9-NITRONAPHTHALENE, 1-NITRO-4-CYCLOHEXYLBENZENE,2-NITROBIPHENYL AND 4NITROBIPHENYL, IN A NON-AQUEOUS, NON-OXIDIZINGSOLVENT MEDIA TO FORM A REACTION MIXTURE,
 2. HEATING SAID REACTONMIXTURE TO BE HYDROGENATED BETWEEN ABOUT 50*C TO ABOUT 135*C, WITH ATLEAST ENOUGH HYDROGEN GAS TO HYDROGENATE ONE NITRO GROUP OF THEDINITROAROMATIC SUBSTRATE TO THE CORRESPONDING AMINE, ATSUPERATMOSPHERIC PRESSURES OF HYDROGEN GAS RANGING FROM ABOUT 100 PSIGTO ABOUT 2,00 PSIG AND IN THE PRESENCE OF AT LEAST A CATALYTIC QUANTITYOF A HOMOGENOUS, SOLUBILIZED RETHENIUM CATALYST SELECTED FROM THE GROUPCONSISTING OF RUCL2(P(C6H5)3)3, (RU(CO)3CL2)2, RUCL2, (CO)2(P(C6H5)3)2,RUCL2(SB(C6H5)3)3, RUCL3(P(C6H5)3)2 AND RUCL3(CH)3(C6H5)3 PBR, UNTILABOUT 80% TO ABOUT 95% OF SAID ONE NITRO GROUP OF DINITROAROMATICSUBSTRATE IS HYDROGENATED TO THE CORRESPONDING AMINE.
 2. heating saidreaction mixture to be hydrogenated between about 50*C to about 135*C,with at least enough hydrogen gas to hydrogenate one nitro group of thedinitroaromatic substrate to the corresponding amine, atsuperatmospheric pressures of hydrogen gas ranging from about 100 psigto about 2,000 psig and in the presence of at least a catalytic quantityof a homogeneous, solubilized ruthenium catalyst selected from the groupconsisting of RuCl2(P(C6H5)3)3, (Ru(CO)3Cl2)2, RuCl2(CO)2(P(C6H5)3)2,RuCl2(Sb(C6H5)3)3, RuCl3(P(C6H5)3)2 and RuCl3(CH)3(C6H5)3PBr, untilabout 80% to about 95% of said one nitro group of dinitroaromaticsubstrate is hydrogenated to the corresponding amine.
 2. The process ofclaim 1 wherein the mixture of nitroaromatics consists ofP-dinitrobenzene and nitrobenzene.
 3. The process of claim 1 wherein themixture of nitroaromatics consists of m-dinitrobenzene and nitrobenzene.4. The process of claim 1 wherein the mixture of nitroaromatics consistsof 1,4-dinitronaphthalene and 1-nitronaphthalene.
 5. The process ofclaim 1 wherein the mixture of nitroaromatics consists of2,6-dinitrotoluene and o-nitrotoluene.
 6. The process of claim 1 whereinthe mixture of nitroaromatics consists of p-dinitrobenzene and1-nitronaphthalene.
 7. The process of claim 1 in which said solventmedia is selected from the group consisting of aromatics, alkyl ethersand chlorinated aliphatic hydrocarbons.
 8. The process of claim 1wherein the non-aqueous solvent media contains a solvent which is a C1to C6 alkanol.
 9. The process of claim 1 wherein the ruthenium catalystis RuCl2(P(C6H5)3)3.
 10. The process of claim 1 wherein the rutheniumcatalyst is RuCl2(CO)2(P(C6H5)3)2.
 11. The process of claim 1 whereinthe ruthenium catalyst is RuCl2(Sb(C6H5)3)3.
 12. The process of claim 1wherein the ruthenium catalyst is RuHCl(P(C6H5)3)3.